1. Field of the Invention
The present invention principally relates to four-cycle engines for powering. outboard motors. More particularly, the present invention relates to cooling and exhaust systems for such engines associated with outboard motors.
2. Description of the Related Art
Outboard motors are often used to power watercraft. The engines are attached to the back of the watercraft and serve to propel as well as push the watercraft. The engines include powerheads that often extend above a transom of the water. Because the engines are not substantially shielded from the front, the engines can be a large source of wind drag. Accordingly, efforts have been made to decrease the size of the outboard motors while not sacrificing engine performance. One way of decreasing the size of outboard motors employing v-type engines is to decrease the spread of the cylinder banks or to decrease the length of the cylinder banks.
A limitation on narrowing the cylinder banks involves the construction of most exhaust systems. The v-type engines currently used in outboard motors often include an exhaust system that routes the exhaust gases through the powerhead and into the drive shaft housing prior to expelling the gases to either the atmosphere or the body of water in which the watercraft is operating. These exhaust systems often include a pair of exhaust manifolds that separately funnel the exhaust gases from selected cylinders through an exhaust guide plate and into the balance of the exhaust system. The manifolds must be properly sized to allow sufficient exhaust gases to flow through the manifolds such that exhaust gas blow down removes sufficient exhaust gases from the combustion chamber. Accordingly, narrowing the valley between the cylinder banks on v-type engines could adversely affect performance due to the decrease in the exhaust manifold cross section.
Additionally, a seal must be maintained between the cylinder block and the exhaust guide plate to avoid gas leakage. Forming a proper seal, however, proves difficult if the sealed surface area becomes too large. Additionally, the cost of materials increases with the increases in the surface area to be sealed. The increase in materials cost is disadvantageous both upon initial sale as well as while completing repair work.